1. Field of the Invention
The invention described herein relates to spectrometers including, for example, spectrometers having gratings monolithically integrated with other optical elements.
2. Description of the Related Art
Spectrometers are optical instruments that determine the spectral content of an optical signal. The output of a spectrometer is a spectral distribution of intensity versus wavelength, referred to herein as a spectrum.
Spectrometers are very useful in a myriad of scientific and technological applications and are the basis of spectroscopy. Spectroscopy may, for example, help identify the composition of materials and may provide information regarding different physical and chemical processes.
Imaging spectrometers are a special type of spectrometer that produces wavelength spectrums for different spatial locations in a two-dimensional field. Imaging spectroscopy can be accomplished by producing spectrums for a plurality of sites along one swath of the two-dimensional field. A recording device, such as an array of photodetectors, is located at an image plane to record the spectral information for locations across the swath. The instrument is then swept over the next swath and the spectral response of each portion of the new swath is measured in a like manner. Spectroscopic information can thereby be obtained for a two-dimensional array of locations.
Spectrometers are used both in the laboratory and in the field. For various applications imaging spectrometers may be included as payloads in satellites, airplanes, or unmanned aerial vehicles (UAVs). Such spectrometers may be used, for example, for remote sensing and reconnaissance. In the case of imaging spectrometers on satellite and airplane platforms, the instrument can be scanned over the two-dimensional field by the motion of the platform itself. In this way, a map over the spectral response of the entire two-dimensional field can be created.
Two characteristics of spectrometers that are therefore desirable are rigidity and small size. Rigidity can be important to ensure that the instrument maintain precise alignment of optical components to achieve desired performance. Over its lifetime the instrument can be subjected to vibration and other physical stresses that can degrade instrument performance if proper alignment of the optical components is lost. These types of physical stresses can occur during rocket launch of a satellite payload or during turbulence or during maneuvering and landing of an airplane or UAV, for example. Small size is also important because space is generally limited for airplane and UAV based instruments and especially in the case of satellite missions where extra size and weight can add significantly to the cost of placing the satellite in orbit. There is a need, therefore, for a spectrometer with increased ruggedness and decreased size.